PROJECT SUMMARY/ABSTRACT Although second-hand tobacco smoke is recognized as a cancer risk, the possibility that living with a smoker fosters a broad household culture of cancer-relevant negative health behaviors is unstudied. Dynamic models of health behavior have considered clustering of different behaviors within individuals and contagion of the same behavior between individuals. Here, we combine these two areas of discovery in proposing a novel process?the possibility that an individual's health behavior may influence another individual's health behavior in a different domain. The proposed project tests an innovative model linking living with a smoker to low physical activity, sedentary behavior, unhealthy diet, and overweight/obesity among middle-aged and older women, a population at risk of exposure to passive-smoking. Our longer-term goal is to develop an R01 application to test a household-level intervention tailored to cross-domain health behaviors among demographically disadvantaged families with a smoker. The objective for the proposed research is to lay a foundation for this planned work by prospectively examining between-individual, cross-domain linkages in overweight/obesity and associated health risk behaviors using data from the Women's Health Initiative (WHI) Observational Study. Our central hypothesis is that individuals' exposure to a household smoker is linked to their own low physical activity, sedentary behavior, unhealthy diet, and overweight/obesity. The rationale for this project is that more rigorous tests of the links between living with a smoker and cancer-relevant negative health behaviors in other domains will provide a foundation for developing more effective cancer prevention strategies. We plan to pursue three specific aims: (1) Examine the role of living with a smoker in predicting overweight/obesity; (2) Identify underlying mechanisms involving health risk behaviors linking living with a smoker to overweight/obesity; and (3) Apply the model to groups of women at increased health risk associated with health disparities and history of cancer. The proposed research is innovative because we examine a neglected social-behavioral pathway in the risk for cancer. Results are expected to have a broader positive impact because understanding the role of social ties in communicating multiple cancer-relevant health habits has potential to advance population health and to reduce health disparities. The contribution of the proposed research is its potential to redirect research and intervention efforts on cancer to an aspect of health behavior change that has been overlooked. This contribution will be significant because it can substantially broaden the reach and effectiveness of preventive efforts for cancer.